Vehicle seat occupancy detection systems are nowadays widely used in vehicles, in particular in passenger cars, for providing a seat occupancy signal for various appliances, for instance for the purpose of a seat belt reminder (SBR) system or an activation control for an auxiliary restraint system (ARS). Seat occupancy detection systems include seat occupancy sensors that are known to exist in a number of variants, e.g. based on capacitive sensing, on deformation sensing or on sensing of pressure/force. In order to meet requirements regarding easy integration and required robustness, weight-sensitive seat occupancy sensors have typically been arranged on the B-surface of a vehicle seat, i.e. between a foam body of a seat cushion and a seat pan or cushion-supporting springs of the vehicle seat.
Further, vehicle seat occupancy detection systems are known to be employed as a means of assessing a potential activation of an installed vehicle passenger restraint system, such as an airbag.
For example, U.S. Pat. No. 5,987,370 describes an apparatus for estimating the weight of an occupant of a seat in a motor vehicle. The apparatus includes a closed elastomeric bladder filled with fluid being installed in the foam cushion of a vehicle seat bottom. The apparatus includes at least one pressure sensor installed in a closed exit port of the bladder. A temperature sensor disposed in proximity to the bladder provides a temperature signal, and a controller estimates the weight of the occupant based on the temperature and pressure signals. The pressure sensor is configured to sense a differential pressure between the fluid and atmospheric pressure at the center of gravity of the fluid in order to provide a stable output independent of changing atmospheric pressure and changing orientation of the bladder due to vehicle pitch and roll. The estimated weight is used as the criteria to distinguish between an adult, an infant or small child.